Showing accurate frequency in digimodes in case of using Fldigi

* Added new configure option: --enable-fldigi-xmlrpc
* Added fldigixmlrpc.[ch] files to read the carrier value of Fldigi
* Modified affected parts of code, when indicated/used the RIG freq:
  * show frequency at right middle part in main window
  * store the correct freq when user grabs the spot
  * restore the correct freq when user loads a station from the bandmap